Managing data deduplication in storage systems based on I/O activities

ABSTRACT

A method is used in managing data deduplication in storage systems based on I/O activities. I/O activity of first and second data objects is evaluated. The first and second data objects are selected for applying a deduplicating technique. Based on the evaluation, the deduplicating technique is applied to the first and second data objects.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending U.S. patent application Ser. No. 14/141,287 entitled MANAGING DATA DEDUPLICATION IN STORAGE SYSTEMS filed on Dec. 26, 2013, and U.S. patent application Ser. No. 14/141,258 entitled MANAGING DATA DEDUPLICATION IN STORAGE SYSTEMS BASED ON STORAGE SPACE CHARACTERISTICS filed on Dec. 26, 2013, which is incorporated herein by reference.

BACKGROUND

1. Technical Field

This application relates to managing data deduplication in storage systems based on I/O activities.

2. Description of Related Art

Computer systems may include different resources used by one or more host processors. Resources and host processors in a computer system may be interconnected by one or more communication connections. These resources may include, for example, data storage devices such as those included in the data storage systems manufactured by EMC Corporation. These data storage systems may be coupled to one or more servers or host processors and provide storage services to each host processor. Multiple data storage systems from one or more different vendors may be connected and may provide common data storage for one or more host processors in a computer system.

A host processor may perform a variety of data processing tasks and operations using the data storage system. For example, a host processor may perform basic system I/O operations in connection with data requests, such as data read and write operations.

Host processor systems may store and retrieve data using a storage device containing a plurality of host interface units, disk drives, and disk interface units. The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels to the storage device and the storage device provides data to the host systems also through the channels. The host systems do not address the disk drives of the storage device directly, but rather, access what appears to the host systems as a plurality of logical disk units. The logical disk units may or may not correspond to the actual disk drives. Allowing multiple host systems to access the single storage device unit allows the host systems to share data in the device. In order to facilitate sharing of the data on the device, additional software on the data storage systems may also be used.

In data storage systems where high-availability is a necessity, system administrators are constantly faced with the challenges of preserving data integrity and ensuring availability of critical system components.

Additionally, the need for high performance, high capacity information technology systems are driven by several factors. In many industries, critical information technology applications require outstanding levels of service. At the same time, the world is experiencing an information explosion as more and more users demand timely access to a huge and steadily growing mass of data including high quality multimedia content. The users also demand that information technology solutions protect data and perform under harsh conditions with minimal data loss and minimum data unavailability. Computing systems of all types are not only accommodating more data but are also becoming more and more interconnected, raising the amounts of data exchanged at a geometric rate.

To address this demand, modern data storage systems (“storage systems”) are put to a variety of commercial uses. For example, they are coupled with host systems to store data for purposes of product development, and large storage systems are used by financial institutions to store critical data in large databases. For many uses to which such storage systems are put, it is highly important that they be highly reliable and highly efficient so that critical data is not lost or unavailable.

Deduplication is a space-saving technology intended to eliminate redundant (duplicate) data (such as, files) on a data storage system. By saving only one instance of a file, disk space can be significantly reduced. For example, a file of size 10 megabytes (MB) may be stored in ten folders of each employee in an organization that has ten employees. Thus, in such a case, 100 megabytes (MB) of the disk space is consumed to maintain the same file of size 10 megabytes (MB). Deduplication ensures that only one complete copy is saved to a disk. Subsequent copies of the file are only saved as references that point to the saved copy, such that end-users still see their own files in their respective folders. Similarly, a storage system may retain 200 e-mails, each with an attachment of size 1 megabyte (MB). With deduplication, the disk space needed to store each attachment of size 1 megabyte (MB) is reduced to just 1 megabyte (MB) from 200 megabyte (MB) because deduplication only stores one copy of the attachment.

Data deduplication can operate at a file or a block level. File deduplication eliminates duplicate files (as in the example above), but block deduplication processes blocks within a file and saves unique copy of each block. For example, if only a few bytes of a document or presentation or a file are changed, only the changed blocks are saved. The changes made to few bytes of the document or the presentation or the file does not constitute an entirely new file.

While deduplication systems have helped make data management much easier, they also come with a number of challenges, especially when managing the process of deduplicating data.

SUMMARY OF THE INVENTION

A method is used in managing data deduplication in storage systems based on I/O activities. I/O activity of first and second data objects is evaluated. The first and second data objects are selected for applying a deduplicating technique. Based on the evaluation, the deduplicating technique is applied to the first and second data objects.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the present invention will become more apparent from the following detailed description of exemplary embodiments thereof taken in conjunction with the accompanying drawings in which:

FIGS. 1-2 are examples of an embodiment of a computer system that may utilize the techniques described herein;

FIG. 3 is an example illustrating storage device layout;

FIG. 4-9 are diagrams illustrating in more detail components that may be used in connection with techniques herein; and

FIG. 10 is a flow diagram illustrating processes that may be used in connection with techniques herein.

DETAILED DESCRIPTION OF EMBODIMENT(S)

Described below is a technique for use in managing data deduplication in storage systems based on I/O activities, which technique may be used to provide, among other things, evaluating I/O activity of first and second data objects, where the first and second data objects are selected for applying a deduplicating technique, and based on the evaluation, applying the deduplicating technique to the first and second data objects.

Generally, a storage extent is a logical contiguous area of storage reserved for a user requesting the storage space. A storage extent may include a set of disks having different RAID levels. A disk may be a physical disk within the storage system. A LUN may be a logical unit number which is an identifier for a logical unit representing a portion of disk storage. Each slice of data may have a mapping to the location of the physical drive where it starts and ends. A LUN presented to a host system may be organized as a file system by a file system mapping logic of a storage system.

A file is uniquely identified by a file system identification number. Each data block of a file is referenced by a logical block number and/or file system block number. A logical block number of a file refers to a data block by relative position of the data block inside the file. A file system block number of a file refers to a data block by relative position of the data block on a physical disk device on which the file is stored. A file system block number for a data block is computed based on a file offset and the size of the data block. Further, an inode of a file includes metadata that provides a mapping to convert a file system block number of a data block to its corresponding logical block number. For example, in case of a data block size of 4 kilobytes (KB), if a file offset value is smaller than 4096 bytes, the file offset corresponds to the first data block of the file, which has file block number 0. Further, for example, if a file offset value is equal to or greater than 4096 bytes and less than 8192 bytes, the file offset corresponds to the second data block of the file, which has file block number 1.

Generally, each file system data block of a file is associated with a respective mapping pointer. A mapping pointer of a file system block points to the file system block and includes metadata information for the file system block. A file system block associated with a mapping pointer may be a data block or an indirect data block which in turn points to other data blocks or indirect blocks. A mapping pointer includes information that help map a logical offset of a file system block to a corresponding physical block address of the file system block.

Further, a mapping pointer of a file system block includes metadata information for the file system block such as a weight that indicates a delegated reference count for the mapping pointer. The delegated reference count is used by a snapshot copy facility when a replica of a file is created. Mapping pointers of the inode of the file are copied and included in the inode of the replica of the file. Mapping pointers of the inode may include mapping pointers pointing to direct data blocks and mapping pointers pointing to indirect data blocks. The delegated reference count values stored in the mapping pointers of the file and the replica of the file are updated to indicate that the file and the replica of the file share data blocks of the file.

The delegated reference counting mechanism is described in U.S. Pat. No. 8,032,498 for “Delegated reference count base file versioning” issued Oct. 4, 2011, which is incorporated herein by reference.

Further, the delegated reference counting mechanism is also used by a deduplication facility for performing deduplication on a set of identical data blocks by sharing the set of identical data blocks and keeping a single copy of data block such that other identical data blocks point to the single copy of the data block.

Thus, a delegated reference count is a way of maintaining block ownership information for indicating whether or not each indirect block or data block of a file is shared with another version of the file or another identical data block. Further, as introduced above, files are organized as a hierarchy of file system blocks including inodes, indirect blocks, and data blocks. The hierarchy of file system blocks includes a parent-child block relationship between a parent object that points to a child object. For example, if the mapping pointer of the inode of a file points to a data block, the association between the mapping pointer of the inode and the data block may be viewed as a parent-child block relationship. Similarly, for example, if the mapping pointer of an indirect block of a file points to a data block, the association between the mapping pointer of the indirect block and the data block may be viewed as a parent-child block relationship. Block ownership information is maintained by storing respective reference counts for the file system indirect blocks and file system data blocks in the file system block hierarchy, and by storing respective delegated reference counts for the parent-child block relationships in the file system block hierarchy. For each parent-child block relationship, a comparison of the respective delegated reference count for the parent-child relationship to the reference count for the child block indicates whether or not the child block is either shared among parent blocks or has a single, exclusive parent block. For example, if the respective delegated reference count is equal to the respective reference count, then the child block is not shared, and the parent block is the exclusive parent of the child block. Otherwise, if the respective delegated reference count is not equal to the respective reference count, then the child block is shared among parent blocks.

Further, when a sharing relationship of a file system block is broken, the reference count in the per-block metadata of the file system block is decremented by the delegated reference count associated with mapping pointer of the file system block.

Data deduplication is a process by which a data storage system can detect multiple identical copies of data and only keep a single copy of that data, thus eliminating the redundant data by removing other copies of that data and thus improving storage utilization. Thus, the data deduplication process has the ability to detect common blocks of data and maintain a single copy of the common blocks, thereby increasing the efficiency of storage devices by storing data in a reduced number of physical blocks. In at least some systems, data deduplication requires iterating over set of data blocks in one or more storage extents of a deduplication domain by processing digest information associated with each data block, finding the data blocks that contain identical information, and mapping the identical data blocks to a single copy of the data. Thus, in a deduplicated system, a single data block may represent a large number such as hundreds of deduplicated data blocks such that each deduplicated data block refers to the single data block stored on a storage device (e.g. a disk). In such systems, an index table of unique digests is created to find commonality among the data set. The size of this index table determines a window of deduplication opportunity. The larger the index table, the more blocks can be checked for duplicates, and thus the larger the opportunity for deduplication.

Generally, a set of storage extents that are deduplicated together form a deduplication domain. During iteration of a deduplication domain, an index table of unique digests is created from data blocks that are iterated through. Further, during iteration of data blocks of a deduplication domain, digest for each data block is computed and compared with digests stored in an index table. If a matching digest for a data block is found in an index table, contents of data blocks are compared to verify that the data blocks are duplicates of each other, and the data block is deduplicated to an identical data block associated with the matching digest found in the index table by updating address mapping information (such as Virtual Block Mapping pointers described herein) of the deduplicated data block to point to the identical data block found using the index table. Further, if no matching digest for a data block is found in an index table, the digest for the data block is added to the index table. Thus, deduplication maps data blocks that contain identical information to a single copy of the data thereby consolidating I/O operations directed to the identical data blocks to the single copy of the data.

In a conventional deduplication system, if a matching digest for a data block is found in an index table, the data block is deduplicated to an identical data block associated with the matching digest found in the index table by simply selecting one data block as a master deduplicated copy, updating the mapping of the other identical data block to point to the selected data block, and freeing storage space associated with the identical data block. Thus, in such a conventional system, the conventional technique of deciding which data block to preserve as a deduplicated block is non-deterministic and a data block may simply be selected for example based on an order in which data blocks are identified. Thus, in such a conventional system, based on the order in which addresses of the data block and identical data blocks are aligned with respect to each other, either the address mapping information of the data block is updated to point to the identical data block found using the index table or the address mapping information of the identical data block found using the index table is updated to point to the data block. Thus, in such a conventional system, a data deduplication process does not take into account characteristics of data blocks when mapping the data blocks to a single identical data block.

For example, in such a conventional system, a deduplicating technique does not take into account a policy such as an I/O access pattern for a data block that has been identified for deduplication. Consequently, in such a conventional system, when a cold data block (data block which is accessed less frequently) and a hot data block (data block which is accessed more frequently) are selected for deduplication, the hot data block may get mapped to the cold data block thereby freeing the hot data block. As a result, in such a conventional system, I/O requests directed to the hot data block are then redirected to the cold data block thereby impacting I/O performance of users of the hot data block. Thus, in such a conventional system, host I/O performance of a hot data block may be degraded after deduplication of the hot data block as references to the hot data block changes thereby causing a change in cache status and mapping information.

By contrast, in at least some implementations in accordance with the technique as described herein, the current technique evaluates I/O access patterns of data objects which have been identified for deduplication. Further, in at least one embodiment of the current technique, when at least two data objects are identified for deduplication, I/O access pattern of the data objects are evaluated to determine which data object is used as a master copy and which data block is mapped to the master copy and freed. Thus, in at least one embodiment of the current technique, I/O mapping path is optimized to continue accessing frequently accessed data after a deduplicating technique is applied.

In at least one embodiment of the current technique, when a deduplicating technique is applied on a set of data objects, hot spots on a storage extent are evaluated such that based on the evaluation, the set of data objects are ordered based on hotness of deduplication candidates during deduplication.

In at least some implementations in accordance with the technique as described herein, the use of the managing data deduplication in storage systems based on I/O activities technique can provide one or more of the following advantages: lowering costs by improving deduplication efficiency, improving memory utilization by evaluating characteristics of data objects identified for deduplication, improving I/O performance of a system by deduplicating data blocks based on I/O activities of the data blocks, and improving host I/O performance by utilizing range lock statistics of storage extents, generating hints for I/O hot spots and using hot spots as a deduplication target during deduplication.

Referring now to FIG. 1, shown is an example of an embodiment of a computer system that may be used in connection with performing the technique or techniques described herein. The computer system 10 includes one or more data storage systems 12 connected to host systems 14 a-14 n through communication medium 18. The system 10 also includes a management system 16 connected to one or more data storage systems 12 through communication medium 20. In this embodiment of the computer system 10, the management system 16, and the N servers or hosts 14 a-14 n may access the data storage systems 12, for example, in performing input/output (I/O) operations, data requests, and other operations. The communication medium 18 may be any one or more of a variety of networks or other type of communication connections as known to those skilled in the art. Each of the communication mediums 18 and 20 may be a network connection, bus, and/or other type of data link, such as hardwire or other connections known in the art. For example, the communication medium 18 may be the Internet, an intranet, network or other wireless or other hardwired connection(s) by which the host systems 14 a-14 n may access and communicate with the data storage systems 12, and may also communicate with other components (not shown) that may be included in the computer system 10. In at least one embodiment, the communication medium 20 may be a LAN connection and the communication medium 18 may be an iSCSI or SAN through fibre channel connection.

Each of the host systems 14 a-14 n and the data storage systems 12 included in the computer system 10 may be connected to the communication medium 18 by any one of a variety of connections as may be provided and supported in accordance with the type of communication medium 18. Similarly, the management system 16 may be connected to the communication medium 20 by any one of variety of connections in accordance with the type of communication medium 20. The processors included in the host computer systems 14 a-14 n and management system 16 may be any one of a variety of proprietary or commercially available single or multiprocessor system, such as an Intel-based processor, or other type of commercially available processor able to support traffic in accordance with each particular embodiment and application.

It should be noted that the particular examples of the hardware and software that may be included in the data storage systems 12 are described herein in more detail, and may vary with each particular embodiment. Each of the host computers 14 a-14 n, the management system 16 and data storage systems may all be located at the same physical site, or, alternatively, may also be located in different physical locations. In connection with communication mediums 18 and 20, a variety of different communication protocols may be used such as SCSI, Fibre Channel, iSCSI, FCoE and the like. Some or all of the connections by which the hosts, management system, and data storage system may be connected to their respective communication medium may pass through other communication devices, such as a Connectrix or other switching equipment that may exist such as a phone line, a repeater, a multiplexer or even a satellite. In at least one embodiment, the hosts may communicate with the data storage systems over an iSCSI or fibre channel connection and the management system may communicate with the data storage systems over a separate network connection using TCP/IP. It should be noted that although FIG. 1 illustrates communications between the hosts and data storage systems being over a first connection, and communications between the management system and the data storage systems being over a second different connection, an embodiment may also use the same connection. The particular type and number of connections may vary in accordance with particulars of each embodiment.

Each of the host computer systems may perform different types of data operations in accordance with different types of tasks. In the embodiment of FIG. 1, any one of the host computers 14 a-14 n may issue a data request to the data storage systems 12 to perform a data operation. For example, an application executing on one of the host computers 14 a-14 n may perform a read or write operation resulting in one or more data requests to the data storage systems 12.

The management system 16 may be used in connection with management of the data storage systems 12. The management system 16 may include hardware and/or software components. The management system 16 may include one or more computer processors connected to one or more I/O devices such as, for example, a display or other output device, and an input device such as, for example, a keyboard, mouse, and the like. A data storage system manager may, for example, view information about a current storage volume configuration on a display device of the management system 16. The manager may also configure a data storage system, for example, by using management software to define a logical grouping of logically defined devices, referred to elsewhere herein as a storage group (SG), and restrict access to the logical group.

It should be noted that although element 12 is illustrated as a single data storage system, such as a single data storage array, element 12 may also represent, for example, multiple data storage arrays alone, or in combination with, other data storage devices, systems, appliances, and/or components having suitable connectivity, such as in a SAN, in an embodiment using the techniques herein. It should also be noted that an embodiment may include data storage arrays or other components from one or more vendors. In subsequent examples illustrated the techniques herein, reference may be made to a single data storage array by a vendor, such as by EMC Corporation of Hopkinton, Mass. However, as will be appreciated by those skilled in the art, the techniques herein are applicable for use with other data storage arrays by other vendors and with other components than as described herein for purposes of example.

An embodiment of the data storage systems 12 may include one or more data storage systems. Each of the data storage systems may include one or more data storage devices, such as disks. One or more data storage systems may be manufactured by one or more different vendors. Each of the data storage systems included in 12 may be inter-connected (not shown). Additionally, the data storage systems may also be connected to the host systems through any one or more communication connections that may vary with each particular embodiment and device in accordance with the different protocols used in a particular embodiment. The type of communication connection used may vary with certain system parameters and requirements, such as those related to bandwidth and throughput required in accordance with a rate of I/O requests as may be issued by the host computer systems, for example, to the data storage systems 12.

It should be noted that each of the data storage systems may operate stand-alone, or may also included as part of a storage area network (SAN) that includes, for example, other components such as other data storage systems.

Each of the data storage systems of element 12 may include a plurality of disk devices or volumes. The particular data storage systems and examples as described herein for purposes of illustration should not be construed as a limitation. Other types of commercially available data storage systems, as well as processors and hardware controlling access to these particular devices, may also be included in an embodiment.

Servers or host systems, such as 14 a-14 n, provide data and access control information through channels to the storage systems, and the storage systems may also provide data to the host systems also through the channels. The host systems do not address the disk drives of the storage systems directly, but rather access to data may be provided to one or more host systems from what the host systems view as a plurality of logical devices or logical volumes. The logical volumes may or may not correspond to the actual disk drives. For example, one or more logical volumes may reside on a single physical disk drive. Data in a single storage system may be accessed by multiple hosts allowing the hosts to share the data residing therein. A LUN (logical unit number) may be used to refer to one of the foregoing logically defined devices or volumes. An address map kept by the storage array may associate host system logical address with physical device address.

In such an embodiment in which element 12 of FIG. 1 is implemented using one or more data storage systems, each of the data storage systems may include code thereon for performing the techniques as described herein. In following paragraphs, reference may be made to a particular embodiment such as, for example, an embodiment in which element 12 of FIG. 1 includes a single data storage system, multiple data storage systems, a data storage system having multiple storage processors, and the like. However, it will be appreciated by those skilled in the art that this is for purposes of illustration and should not be construed as a limitation of the techniques herein. As will be appreciated by those skilled in the art, the data storage system 12 may also include other components than as described for purposes of illustrating the techniques herein.

The data storage system 12 may include any one or more different types of disk devices such as, for example, an ATA disk drive, FC disk drive, and the like. Thus, the storage system may be made up of physical devices with different physical and performance characteristics (e.g., types of physical devices, disk speed such as in RPMs), RAID levels and configurations, allocation of cache, processors used to service an I/O request, and the like.

Given the different performance characteristics, one or more tiers of storage devices may be defined. The physical devices may be partitioned into tiers based on the performance characteristics of the devices; grouping similar performing devices together. Conversely, the particular performance characteristics may be applied to a storage pool with or without the definition of tiers. The set of resources associated with or designated for use by a tier or grouping within a pool may be characterized as a dynamic binding in that the particular set of data storage system resources utilized by consumers in a tier may vary from time to time. A current configuration for the data storage system, static aspects of the current data storage system resources (e.g., types of devices, device storage capacity and physical device characteristics related to speed and time to access data stored on the device), and current workload and other dynamic aspects (e.g., actual observed performance and utilization metrics) of the data storage system may vary at different points in time.

In certain cases, an enterprise can utilize different types of storage systems to form a complete data storage environment. In one arrangement, the enterprise can utilize both a block based storage system and a file based storage hardware, such as a VNX™ or VNXe™ system (produced by EMC Corporation, Hopkinton, Mass.). In such an arrangement, typically the file based storage hardware operates as a front-end to the block based storage system such that the file based storage hardware and the block based storage system form a unified storage system.

Referring now to FIG. 2, shown is an example of an embodiment of a computer system such as a unified data storage system that may be used in connection with performing the technique or techniques described herein. As shown, the unified data storage system 10 includes a block based storage system 12 and file based storage hardware 34. While the block based storage system 12 may be configured in a variety of ways, in at least one embodiment, the block based storage system 12 is configured as a storage area network (SAN), such as a VNX™ or VNXe™ system, as produced by EMC Corporation of Hopkinton, Mass. While the file based storage hardware 34 may be configured in a variety of ways, in at least one embodiment, the file based storage hardware 34 is configured as a network attached storage (NAS) system, such as a file server system produced by EMC Corporation of Hopkinton, Mass., configured as a header to the block based storage system 12.

The computer system 10 includes one or more block based data storage systems 12 connected to host systems 14 a-14 n through communication medium 18. The system 10 also includes a management system 16 connected to one or more block based data storage systems 12 through communication medium 20. In this embodiment of the computer system 10, the management system 16, and the N servers or hosts 14 a-14 n may access the block based data storage systems 12, for example, in performing input/output (I/O) operations, data requests, and other operations. The communication medium 18 may be any one or more of a variety of networks or other type of communication connections as known to those skilled in the art. Each of the communication mediums 18 and 20 may be a network connection, bus, and/or other type of data link, such as a hardwire or other connections known in the art. For example, the communication medium 18 may be the Internet, an intranet, network or other wireless or other hardwired connection(s) by which the host systems 14 a-14 n may access and communicate with the block based data storage systems 12, and may also communicate with other components (not shown) that may be included in the computer system 10. In one embodiment, the communication medium 20 may be a LAN connection and the communication medium 18 may be an iSCSI or fibre channel connection.

Each of the host systems 14 a-14 n and the block based data storage systems 12 included in the computer system 10 may be connected to the communication medium 18 by any one of a variety of connections as may be provided and supported in accordance with the type of communication medium 18. Similarly, the management system 16 may be connected to the communication medium 20 by any one of variety of connections in accordance with the type of communication medium 20. The processors included in the host computer systems 14 a-14 n and management system 16 may be any one of a variety of proprietary or commercially available single or multiprocessor system, such as an Intel-based processor, or other type of commercially available processor able to support traffic in accordance with each particular embodiment and application.

In at least one embodiment of the current technique, block based data storage system 12 includes multiple storage devices 40, which are typically hard disk drives, but which may be tape drives, flash memory, flash drives, other solid state drives, or some combination of the above. In at least one embodiment, the storage devices may be organized into multiple shelves 44, each shelf containing multiple devices. In the embodiment illustrated in FIG. 2, block based data storage system 12 includes two shelves, Shelf1 44A and Shelf2 44B; Shelf1 44A contains eight storage devices, D1-D8, and Shelf2 also contains eight storage devices, D9-D16.

Block based data storage system 12 may include one or more storage processors 46, for handling input/output (I/O) requests and allocations. Each storage processor 46 may communicate with storage devices 40 through one or more data buses 48. In at least one embodiment, block based data storage system 12 contains two storage processors, SP1 46A, and SP2 46B, and each storage processor 46 has a dedicated data bus 48 for each shelf 44. For example, SP1 46A is connected to each storage device 40 on Shelf1 44A via a first data bus 48A and to each storage device 40 on Shelf2 44B via a second data bus 48B. SP2 46B is connected to each storage device 40 on Shelf1 44A via a third data bus 48C and to each storage device 40 on Shelf2 44B via a fourth data bus 48D. In this manner, each device 40 is configured to be connected to two separate data buses 48, one to each storage processor 46. For example, storage devices D1-D8 may be connected to data buses 48A and 48C, while storage devices D9-D16 may be connected to data buses 48B and 48D. Thus, each device 40 is connected via some data bus to both SP1 46A and SP2 46B. The configuration of block based data storage system 12, as illustrated in FIG. 2, is for illustrative purposes only, and is not considered a limitation of the current technique described herein.

In addition to the physical configuration, storage devices 40 may also be logically configured. For example, multiple storage devices 40 may be organized into redundant array of inexpensive disks (RAID) groups. Although RAID groups are composed of multiple storage devices, a RAID group may be conceptually treated as if it were a single storage device. As used herein, the term “storage entity” may refer to either a single storage device or a RAID group operating as a single storage device.

Storage entities may be further sub-divided into logical units. A single RAID group or individual storage device may contain one or more logical units. Each logical unit may be further subdivided into portions of a logical unit, referred to as “slices”. In the embodiment illustrated in FIG. 2, storage devices D1-D5, is sub-divided into 3 logical units, LU1 42A, LU2 42B, and LU3 42C. The LUs 42 may be configured to store a data file as a set of blocks striped across the LUs 42.

The unified data storage system 10 includes a file based storage hardware 34 that includes at least one data processor 26. The data processor 26, for example, may be a commodity computer. The data processor 26 sends storage access requests through physical data link 36 between the data processor 26 and the block based storage system 12. The data link 36 may be any one or more of a variety of networks or other type of communication connections as known to those skilled in the art. The processor included in the data processor 26 may be any one of a variety of proprietary or commercially available single or multiprocessor system, such as an Intel-based processor, or other type of commercially available processor able to support traffic in accordance with each particular embodiment and application. Further, file based storage hardware 34 may further include control station 30 and additional data processors (such as data processor 27) sharing storage device 40. A dual-redundant data link 32 interconnects the data processors 26, 27 to the control station 30. The control station 30 monitors a heartbeat signal from each of the data processors 26, 27 in order to detect a data processor failure. If a failed data processor cannot be successfully re-booted, the control station 30 will “fence off” the failed data processor and re-assign or fail-over the data processing responsibilities of the failed data processor to another data processor of the file based storage hardware 34. The control station 30 also provides certain server configuration information to the data processors 26, 27. For example, the control station maintains a boot configuration file accessed by each data processor 26, 27 when the data processor is reset.

The data processor 26 is configured as one or more computerized devices, such as file servers, that provide end user devices (not shown) with networked access (e.g., NFS and CIFS facilities) to storage of the block based storage system 12. In at least one embodiment, the control station 30 is a computerized device having a controller, such as a memory and one or more processors. The control station 30 is configured to provide hardware and file system management, configuration, and maintenance capabilities to the data storage system 10. The control station 30 includes boot strap operating instructions, either as stored on a local storage device or as part of the controller that, when executed by the controller following connection of the data processor 26 to the block based storage system 12, causes the control station 30 to detect the automated nature of a file based storage hardware installation process and access the data processor 26 over a private internal management network and execute the file based hardware installation process.

FIG. 3 illustrates one of the many ways of constructing storage extents from a group of physical devices. For example, RAID Group 64 may be formed from physical disk devices 60. The data storage system best practices of a policy may specify the particular RAID level and configuration for the type of storage extent being formed. The RAID Group 64 may provide a number of data storage LUNs 62. An embodiment may also utilize one or more additional logical device layers on top of the LUNs 62 to form one or more logical device volumes 61. The particular additional logical device layers used, if any, may vary with the data storage system. It should be noted that there may not be a 1-1 correspondence between the LUNs of 62 and the volumes of 61. In a similar manner, device volumes 61 may be formed or configured from physical disk devices 60. Device volumes 61, LUNs 62 and physical disk devices 60 may be configured to store one or more blocks of data or one or more files organized as a file system. A storage extent may be formed or configured from one or more LUNs 62. Thus, a deduplication domain consists of a set of storage extents which includes a set of deduplicated LUNs sharing a common set of blocks.

The data storage system 12 may also include one or more mapped devices 70-74. A mapped device (e.g., “thin logical unit”, “direct logical unit”) presents a logical storage space to one or more applications running on a host where different portions of the logical storage space may or may not have corresponding physical storage space associated therewith. However, the “thin logical unit” (“TLU”) mapped device is not mapped directly to physical storage space. Instead, portions of the mapped storage device for which physical storage space exists are mapped to data devices such as device volumes 61 a-61 b, which are logical devices that map logical storage space of the data device to physical storage space on the physical devices 60 a-60 b. Thus, an access of the logical storage space of the “thin logical unit” (“TLU”) mapped device results in either a null pointer (or equivalent) indicating that no corresponding physical storage space has yet been allocated, or results in a reference to a data device which in turn references the underlying physical storage space.

Referring to FIG. 4, shown is a more detailed representation of components that may be included in an embodiment using the techniques herein. With reference also to FIGS. 1-3, in a deduplication domain, each storage extent contains a range of data blocks. For example, in FIG. 4, storage extent A 131, storage extent B 132 and storage extent C 133 are part of the deduplication domain-1 130. Within a data storage system, there may be multiple deduplication domains such as deduplication domain-1 130, and other deduplication domains. Within a deduplication domain, a goal of a deduplication process is to maintain only a single copy of each unique set of data. Software or other logic executing the deduplication process examines data in the deduplication domain in fixed sized chunks and determines whether the data stored in a chunk is the same as the data stored in another chunk in the same deduplication domain. If so, an address map for the LUNs is manipulated so that respective address map entries for the chunks reference the same physical chunk of data, and then the chunks that currently hold the extra copies of the data are freed up as unused storage. The address map for the LUNs stores a mapping of logical block addresses to physical block addresses. In at least some embodiments of the current technique, the fixed sized chunk can be a data block. For example, in FIG. 4, storage extent A 131 includes data blocks 134-137, storage extent B 132 includes data blocks 138-141 and storage extent C 131 includes data blocks 142-145 and other data blocks (not shown).

In at least one embodiment of the current technique, deduplication logic can be provided on data storage system 12. In an alternative embodiment, deduplication logic may be provided also or instead on a host system, such as host system 14. As described elsewhere herein, deduplication logic may be performed in a manner that is transparent to an application running on a host system. In at least one embodiment of the current technique, deduplication server 110 provides deduplication services in data storage system 12 by working in conjunction with I/O Coordinator 155 and File system mapping driver 165. I/O Coordinator 155 manages I/O operations in conjunction with the file system mapping driver 165. I/O Coordinator 155 provides framework for implementing digest and other I/O requests issued by the deduplication server 110. File system mapping driver 165 is a light-weight file system library that provides file system functionality and allows data storage system 12 to create files within a file system. File system mapping driver 165 processes I/Os directed to metadata of a file system and provides information regarding metadata (e.g., deduplication key, data block mapping information) of a data block that is potentially a candidate for deduplication.

In at least one embodiment of the current technique, deduplication director 120 is a process that iterates through deduplication domains including logical units and schedules data deduplication processes based on deduplication policies 122 to perform data deduplication. Further, deduplication director 120 works in conjunction with deduplication engine 105 to perform data deduplication on deduplication domain 130. Thus, deduplication director 120 is a component responsible for coordinating data deduplication operations. As a result, deduplication director 120 identifies data deduplication domains, manages storage space for performing data deduplication, and manages deduplication engine 105 to process each data deduplication domain.

In at least one embodiment of the current technique, deduplication server 110 is a component that provides services to deduplication director 120 to iterate over sets of data in a set of deduplication domain 130. Deduplication server 110 also computes digests and remaps blocks after the deduplication technique is applied to remove duplicate blocks of data. A deduplication database (e.g. an index table) is maintained for a deduplication domain. Deduplication engine 105 communicates with the deduplication server 110 to iterate through the set of deduplication domain 130 and computes digests for data blocks that are iterated through. A digest is created for each chunk of data (e.g., a data block) that is identified as a candidate for deduplication. Deduplication engine 105 detects potential duplicate copies of data and issues a request to the deduplication server 110 to deduplicate the data. The deduplication database is stored on one of the storage extents that include one or more LUNs. An index table 115 may also be maintained on a LUN located in the same pool as the deduplication domain 130. In at least some implementations, an index table is a persistent hash-table of chunk-IDs keyed by the digest of the data stored in the chunk. The index table need not contain entries for every data chunk in the deduplication domain, but the effectiveness of deduplication is a function of the number of entries stored in the index table 115. The more entries in the index table, the more likely that duplicate blocks will be detected during deduplication processing.

During deduplication processing as described herein, deduplication server 110 provides services to deduplication engine 105 by interacting with I/O coordinator 155 and file system mapping driver 165. Deduplication of data happens in two logically distinct operations: detection and remapping. The detection operation identifies blocks containing the same data. The remapping operation updates address maps that record physical locations of logical units of data so that a single block of data is shared by multiple LUNs or by multiple positions within the same LUN. Detection is accomplished by building a database (e.g., index table 115) that maintains a digest (e.g., SHA, checksum) for each block. When two blocks have the same digest they have a sufficiently high probability of containing the same data to warrant a bit-for-bit comparison to confirm they are exact duplicates. Remapping leverages dynamic block-mapping technology of file system mapping driver 165. A file system allows dynamic manipulation of the address maps that connects LUN's logical address space to its physical address space. The file system also allows mapping a single block of storage at multiple locations within the file system, and allows handling of writes to shared blocks by allocating new storage and updating the shared address mappings. Further, a file system may use a virtual block mapping pointers (also referred to herein as “VBM pointers”) to map a data block. I/O coordinator 155 manages I/O operations in conjunction with the file system mapping driver 165. I/O coordinator 155 provides framework for implementing digest and other I/O requests issued by the deduplication server 110.

Thus, deduplication engine 105 and deduplication server 110 working in conjunction with one another identify data blocks for deduplication, compare data digest information of the data blocks, identify candidate data blocks for deduplication, issue deduplication requests, and maintain index table 115. Further, I/O coordinator 155 and file system mapping driver 165 working in conjunction with one another process deduplication requests received from deduplication server 110. File system mapping driver 165 performs a deduplication operation by updating VBM pointers of a deduplicated data block and freeing up redundant instances of the deduplicated data block.

In at least one embodiment of the current technique, deduplication engine 105 and deduplication server 110 working in conjunction with one another identify data blocks for deduplication. Further, in at least one embodiment of the current technique, when data blocks are identified for deduplication, characteristics of I/O access pattern for the data blocks are evaluated based on a deduplication policy in such a way that a data block having a high number of I/O operations is used for deduplicating other identical instances of the data block.

It should be noted that a set of deduplication policies may be initialized and selected by a data storage system. Further, it should be noted that a set of deduplication policies may be selected by a user of a data storage system.

In at least one embodiment of the current technique, data storage system 12 receives host IOs from host systems 14. In order to maintain data consistency, the data storage system 12 imposes locks on storage extents when processing host IOs. For example, the data storage system 12 applies read (or shared) locks on ranges of extents when the host systems 14 read host data from these ranges of extents. Furthermore, the data storage system 12 applies write (or exclusive) locks on ranges of extents when the host systems 14 write host data to these ranges of extents. Thus, IO hot spots are identified based on ranges of extents of host IO operations. In particular, as host IO operations access ranges of extents on a data storage system, locks on these ranges which are used to synchronize access to data (e.g., between a host IO operation and other system activities) can be tracked by a lock history database. As the data storage system 12 imposes range locks on the ranges of extents, the data storage system 12 updates contents of a lock history database based on these range locks. Accordingly, the data storage system 12 is then able to identify which extents are active (or inactive) based on the contents of the lock history database. With the contents of the lock history database now available for analysis, the contents of the lock history database are able to identify particular extents which are active and inactive. Thus, IO hot spots (i.e., active storage extents) can then be identified from the information in the lock history database, and data storage services can be configured to smartly operate based on the identified IO hot spots such as an automated data placement service which places data among storage tiers and deduplication services which selects a data block associated with the most I/O activity as a master copy for deduplicating other identical instances of data blocks.

In at least one embodiment of the current technique, a lock history database includes range-lock entries, each range-lock entry identifying a respective host IO operation and a respective range of extents which was locked by the respective host IO operation. In such a case, updating the contents of the lock history database includes receiving an IO event message indicating a particular host IO operation and a particular range of extents which was accessed by the particular host IO operation, and adding a new range-lock entry to the lock history database. The new range-lock entry identifies the particular host IO operation and the particular range of extents which was locked by the particular host IO operation.

In at least one embodiment of the current technique, a range of extents is defined by a starting offset and an extent length. In another embodiment of the current technique, a range of extents is defined by a starting offset and an ending offset. Alternative ways of defining a range of extents are suitable for use as well.

The range lock mechanism is described in U.S. patent application Ser. No. 13/536,389 for “Techniques for Identifying IO Hot Spots Using Range-Lock Information” filed on Jun. 28, 2012, which is incorporated herein by reference.

Referring to FIG. 5, shown is a logical representation of a LUN presented to a host and organized as a file system that may be included in an embodiment using the techniques herein. A user of data storage system 12 accesses data from LUNs stored on disk drives 60 in fixed sized chunks. Each fixed size chunk is known as a slice. One or more slices are grouped together to create a slice pool. Host system 14 provisions storage from slice pools for creating LUNs. A LUN 80 is visible to host system 14 and a user of a data storage system 12. Typically, storage is allocated when host system 14 issues a write request and needs a data block to write user's data. File systems typically include metadata describing attributes of a file system and data from a user of the file system. A file system contains a range of file system blocks that store metadata and data. A file system mapping driver 165 allocates file system blocks from slices of storage for creating files and storing metadata of a file system. In at least some embodiments of the current technique, the file system block may be 8 kilobyte (KB) in size. Further, a user of data storage system 12 creates files in a file system. The file system is organized as a hierarchy. At the top of the hierarchy is a hierarchy of the directories 82 in the file system. Inodes of data files 84 depend from the file system directory hierarchy 82. Indirect blocks of data files 86 depend from the inodes of the data files 84. Data block metadata 87 and data blocks of data files 88 depend from the inodes of data files 84 and from the indirect blocks of data files 86.

A file system includes one or more file system blocks. Some of the file system blocks are data blocks, some file system blocks may be indirect block, as described above, or some file system blocks are free blocks that have not yet been allocated to any file in the file system. In an indirect mapping protocol, such as the conventional indirect mapping protocol of a UNIX-based file system, the indirect mapping protocol permits any free block of the file system to be allocated to a file of the file system and mapped to any logical block of a logical extent of the file. This unrestricted mapping ability of the conventional indirect mapping protocol of a UNIX-based file system is a result of the fact that metadata for each file includes a respective pointer to each data block of the file of the file system, as described below. Each file of the file system includes an inode containing attributes of the file and a block pointer array containing pointers to data blocks of the file. There is one inode for each file in the file system. Each inode can be identified by an inode number. Several inodes may fit into one of the file system blocks. The inode number can be easily translated into a block number and an offset of the inode from the start of the block. Each inode of a file contains metadata of the file. Some block pointers of a file point directly at data blocks, other block pointers of the file points at blocks of more pointers, known as an indirect block. There are at least fifteen block pointer entries in a block pointer array contained in an inode of a file. The first of up to twelve entries of block pointers in the inode directly point to the first of up to twelve data blocks of the file. If the file contains more than twelve data blocks, then the thirteenth entry of the block pointer array contains an indirect block pointer pointing to an indirect block containing pointers to one or more additional data blocks. If the file contains so many data blocks that the indirect block becomes full of block pointers, then the fourteenth entry of the block pointer array contains a double indirect block pointer to an indirect block that itself points to an indirect block that points to one or more additional data blocks. If the file is so large that the indirect block becomes full of block pointers and its descendant indirect blocks are also full of block pointers, then the fifteenth entry of the block pointer array includes another level of indirection where the block pointer entry contains a triple indirect block pointer to an indirect block that points to an indirect block that points to an indirect block that points to one or more additional data blocks. Similarly there exists fourth and fifth level of indirections. Once the indirect blocks at last level of indirection and its descendant indirect blocks become full of pointers, the file contains a maximum permitted number of data blocks. Further, an indirect block at the last level of indirection is also referred to as a leaf indirect block. However, it should be noted that a file system may be organized based on any one of the known mapping techniques such as an extent based binary tree mapping mechanism.

Referring to FIG. 6, shown is a representation of a per block metadata (also referred to as “BMD”) for a file system data block that may be included in an embodiment using the techniques described herein. The per-block metadata 70 for a file system data block includes an inode number of a file of the file system, the file system data block number and the logical offset of the file system data block. The per-block metadata 70 for a file system data block also includes an internal checksum protecting the integrity of the information stored in the per-block metadata 70. The per-block metadata for a file system data block may further include a mapping pointer 71 and a data structure indicating state of the per-block metadata 72.

Referring to FIG. 7, shown is a representation of a mapping pointer 71 of a file system data block that may be included in an embodiment using the techniques described herein. Each file system data block of a file is associated with a respective mapping pointer. A mapping pointer of a file system block points to the file system block and includes metadata information for the file system block. A file system block associated with a mapping pointer may be a data block or an indirect data block which in turn points to other data blocks or indirect blocks. A mapping pointer includes information that help map a logical offset of a file system block to a corresponding physical block address of the file system block. Mapping pointer 71 includes metadata information such as shared bit 90, digest bit 91, direct bit 92, virtual bit 93, weight 94, unused bit 95 and block address 96. Shared bit 90 of mapping pointer 71 associated with a file system data block indicates whether the data block (or data blocks if the mapping pointer is associated with an indirect block) may be shared. Digest bit 91 of mapping pointer 71 for a file system block indicates whether the file system block has been digested by a deduplication engine. Direct bit 92 of mapping pointer 71 for a file system block indicates whether the physical address of the file system block can be computed algorithmically. Virtual bit 93 of mapping pointer 71 for a file system block indicates whether the mapping pointer is a virtual pointer. Weight 94 of mapping pointer 71 for a file system block indicates a delegated reference count for the mapping pointer 71. The delegated reference count is used by a snapshot copy facility when a replica of a file is created. Mapping pointers of the inode of the file are copied and included in the inode of the replica of the file. In at least one embodiment, mapping pointers of the inode may include mapping pointers pointing to direct data blocks and mapping pointers pointing to indirect data blocks. Then, the delegated reference count values stored in the mapping pointers of the file and the replica of the file are updated to indicate that the file and the replica of the file share data blocks of the file. Further, the delegated reference count may also be used by a deduplicating technique to deduplicate identical data blocks of a source and target logical objects. Unused bit 95 of mapping pointer 71 for a file system block indicates an unused space reserved for a future use. Block address 96 of mapping pointer 71 for a file system block indicates the block number of the file system block. Alternatively, block address 96 of mapping pointer 71 may indicate a Virtual Block Metadata (“VBM”) identification number which points to a VBM object that points to a data block and includes metadata for the data block. Thus, VBM Id 96 is used to find an object including virtual block metadata. Thus, a VBM object includes file system data block mapping pointer as described in FIG. 7. It also includes a total distributed weight for the VBM object which is the sum of weights of each mapping pointer for a file system block pointing to the VBM object. The VBM object may further includes a mapping pointer which may point to a file system block or another VBM object such that the mapping pointer includes the distributed weight for the mapping pointer.

In response to a request by a client of a storage system to de-duplicate a file system block or to create a snapshot copy of a production file, a virtual block mapping pointer is created that provides a mapping information to a logical block storing data of the file system block of the production file. The file system block includes a pointer pointing back to the metadata of the virtual block mapping pointer. Thus, a new kind of block pointer called virtual block mapping (VBM) pointer enables a migration or re-organization of data blocks to be performed in a non-disruptive fashion that is transparent to a file system manager because pointers to logical data blocks may be changed dynamically without having to change block pointers in inodes and indirect blocks pointing to the data blocks.

In at least one embodiment of the current technique, source and target data blocks are deduplicated by updating VBM pointers of the source and target data blocks such that at the completion of a deduplication operation, the VBM pointer of the target data block points to the VBM pointer of the source data block and the target data block is freed if the target data block is not shared by any other mapping pointer.

Referring to FIG. 8, shown is a more detailed representation of components that may be included in an embodiment using the techniques described herein. FIG. 8 shows mapping pointers 200, 210 for source and target data blocks that are identified for deduplicating the source data block 230 and the target data block 235. The mapping pointer 200 for the source data block 230 includes shared bit 201 indicating that the source data block has not been shared yet, virtual bit 202, direct bit 203, digest bit 204, delegated reference count (e.g., for illustration purposes a value denoted by “d1”) 205 and VBM identification number 206 pointing to VBM object 220. The delegated reference count 205 value may be a specific number such as 20 or 1,000. The source data block 230 has associated per-block metadata including a reference count 231. The per-block metadata of the source data block 230, for example, may be organized as a table separate from the source data block 230 and indexed by the block number of the source data block 230.

The VBM object 220 includes metadata for data block 230 such as is de-duped field 221 indicating whether the data block 230 has been deduplicated, total distributed weight 222 indicating the sum of reference counts of data blocks referenced by the VBM object 220, and mapping pointer 223 to data block 230. For example, in FIG. 8, weight (“d1”) 205 included in mapping pointer 200 and total distributed weight (“d1”) 222 included in the VBM object 220 indicates that the VBM object 220 is owned by the mapping pointer 200. Similarly, weight (“d4”) included in mapping pointer 223 of the VBM object 220 and weight (“d4”) 231 included in per-block metadata of data block 230 indicates that the data block 230 is owned by the VBM object 220. Thus, in such a case, the data block 230 is owned by mapping pointer 200 by an indirect reference as each mapping pointer in the chain from mapping pointer 200 to data block 230 owns the object pointed to by respective mapping pointer.

Similarly, the mapping pointer 210 for the target data block 235 includes shared bit 211 indicating that the target data block has not been shared yet, virtual bit 212, direct bit 213, digest bit 214, delegated reference count (e.g., for illustration purposes a value denoted by “d2”) 215 and VBM identification number 216 pointing to VBM object 225. The delegated reference count 215 value may be a specific number such as 20 or 1,000. The target data block 235 has associated per-block metadata including a reference count 236. The per-block metadata of the target data block 235, for example, is organized as a table separate from the target data block 235 and indexed by the block number of the target data block 235.

The VBM object 225 includes metadata for data block 235 such as total distributed weight 226 indicating the sum of reference counts of mapping pointers referenced by the VBM object 225, and mapping pointer 227 to data block 235. In the example of FIG. 8, the delegated reference count 215 has an initial full-weight value (e.g. d2 which may be, for example, 1000) and the reference count 236 in the per-block metadata of the target data block 235 also has an initial full-weight value (e.g. d3 which may be, for example, 1000). Further, weight (“d2”) 215 matches with total distributed weight (“d2”) 226 in the VBM object indicating that mapping pointer 210 owns the VBM object 225 which in turns own the data block 235 because of the matching weight values in mapping pointer 227 and data block 235.

Referring to FIG. 9, shown is a more detailed representation of components that may be included in an embodiment using the techniques described herein. With reference also to FIG. 8, in at least one embodiment of the current technique, source data block 230 is deduplicated to target data block 235 by updating metadata such as VBM objects 220, 225 and mapping pointer 227 using the delegated reference counting mechanism based on the determination that I/O activity for the target data block 235 is less than I/O activity for the source data block 230. Thus, a deduplicating technique selects the source data block 230 as a master copy and deduplicate the target data block 235 to the source data block 230 based on evaluation of I/O activities of the source and target data blocks 230, 235 which may be evaluated based on range-lock information.

In order to perform deduplication of target data block 235 to source data block 230, the source data block 230 is shared by mapping pointer 200 of the source data block 230 and mapping pointer 210 of target data block 235. The sharing of the source data block 230 is performed by updating mapping pointer 227 in VBM object 225 for the target data block such that the mapping pointer 227 points to VBM object 220 for the source data block 230. Total distributed weight 222 for VBM object 220 for source data block 230 is incremented by total distributed weight value 226 in VBM object 225 of target data block 235 to indicate that VBM object 220 is now shared between mapping pointers 200, 210 of source and target data blocks 230, 235. The shared bit 201 of mapping pointer 200 for the source data block 230 is updated to indicate that contents of source data block 230 are now shared which further indicates that the VBM object 220 referenced by mapping pointer 200 is now shared by the mapping pointer 200 and VBM object 225. Further, is de-duped field 221 in VBM object 220 for source data block 230 is set to indicate that the source data block has been deduplicated to indicate that now identical data block (such as target data block 235) shares the source data block 230. Thus, the target logical object is deduplicated to the source logical object.

Thus, a data de-duplication facility using the current technique changes the mapping pointer 227 in the VBM object 225 for target data block 235 (which has been identified as a cold data block) to point to VBM object 220 for the source data block 230 (which has been identified as a hot data block), and increments the total distributed weight 222 in the VBM object 220 for the source data block 230 by reference count value (e.g. “d3”) 236 of target data block 235. At the end of the deduplication operation, if the target data block 235 is not shared by any other mapping pointer for a file system block, the target data block 235 is freed. For example, in FIG. 9, at the end of the deduplication operation, VBM object 225 no longer points to data block 235. Thus, in such a case, the data block 235 is freed because the VBM object 225 that previously owned the data block 235 no longer points to the data block 235.

Referring to FIG. 10, shown is a flow diagram illustrating a flow of data in the data storage system. With reference also to FIGS. 1-9, data deduplication is managed in a storage system based on I/O activities of logical objects (e.g., storage extents, range of extents, data blocks) (step 450). A request is received to deduplicate a first data object to a second data object (step 452). I/O activity of the first and second data objects is evaluated (step 454). Based on the evaluation of the I/O activities for both data objects, a deduplicating technique is applied to the first and second data objects (step 456). In such a case, a hot data object having a high number of I/O activities is selected as a master copy during a deduplication operation.

While the invention has been disclosed in connection with preferred embodiments shown and described in detail, their modifications and improvements thereon will become readily apparent to those skilled in the art. Accordingly, the spirit and scope of the present invention should be limited only by the following claims. 

What is claimed is:
 1. A method for use in managing data deduplication in storage systems based on I/O activities, the method comprising: evaluating input/output (I/O) operations activity of first and second data objects based on I/O access patterns for the first and second data objects, wherein the first and second data objects are selected for applying a deduplicating technique; and based on the evaluation, applying the deduplicating technique to the first and second data objects, wherein applying the deduplicating technique includes updating mapping information of the first and second data objects, wherein the second data object is deduplicated to the first data object upon determining that I/O operations activity for the first data object is higher than I/O operations activity for the second data object, wherein the first data object is deduplicated to the second data object upon determining that I/O operations activity for the second data object is higher than I/O operations activity for the first data object.
 2. The method of claim 1, wherein the first and second data objects are selected from the group consisting of a deduplication domain, a storage extent, a Logical Unit Number (LUN), a file and a data block, wherein the data block is a fixed size chunk of a physical disk storage.
 3. The method of claim 2, wherein a deduplication domain comprises a set of storage extents, wherein each storage extent of the set of storage extents comprises a set of LUNs, each LUN of the set of LUNs is a logical representation of a subset of physical disk storage.
 4. The method of claim 1, wherein a mapping pointer is associated with a data block, wherein the mapping pointer includes a distributed weight indicating whether the data block has been shared.
 5. The method of claim 1, wherein a mapping pointer for a data block points to a Virtual Block Mapping object, wherein the Virtual Block Mapping object includes another mapping pointer to refer to a data block and a total distributed weight indicating whether the Virtual Block Mapping object has been shared.
 6. The method of claim 1, further comprising: based on the evaluation of I/O activity of the first and second data objects, determining whether to keep the first data object as a master deduplicated data object; based on the determination, updating a Virtual Block Mapping object referred to by a mapping pointer of the second data object by changing the mapping pointer included in the Virtual Block Mapping object to point to a Virtual Block Mapping object referred to by a mapping pointer of the first data object; and freeing the second data object.
 7. The method of claim 6, further comprising: updating a total distributed weight of the Virtual Block Mapping object referred to by the mapping pointer of the first data object.
 8. The method of claim 1, wherein a master deduplicated copy is selected from the group consisting of the first and second data objects based on evaluation of the I/O activity of the first and second data objects.
 9. The method of claim 1, wherein the first data object is selected as a master deduplicated copy upon determining that I/O activity of the first data object is more than I/O activity of the second data object.
 10. A system for use in managing data deduplication in storage systems based on I/O activities, the system comprising: first logic evaluating input/output (I/O) operations activity of first and second data objects based on I/O access patterns for the first and second data objects, wherein the first and second data objects are selected for applying a deduplicating technique; and second logic applying, based on the evaluation, the deduplicating technique to the first and second data objects, wherein applying the deduplicating technique includes updating mapping information of the first and second data objects, wherein the second data object is deduplicated to the first data object upon determining that I/O operations activity for the first data object is higher than I/O operations activity for the second data object, wherein the first data object is deduplicated to the second data object upon determining that I/O operations activity for the second data object is higher than I/O operations activity for the first data object.
 11. The system of claim 10, wherein the first and second data objects are selected from the group consisting of a deduplication domain, a storage extent, a Logical Unit Number (LUN), a file and a data block, wherein the data block is a fixed size chunk of a physical disk storage.
 12. The system of claim 11, wherein a deduplication domain comprises a set of storage extents, wherein each storage extent of the set of storage extents comprises a set of LUNs, each LUN of the set of LUNs is a logical representation of a subset of physical disk storage.
 13. The system of claim 10, wherein a mapping pointer is associated with a data block, wherein the mapping pointer includes a distributed weight indicating whether the data block has been shared.
 14. The system of claim 10, wherein a mapping pointer for a data block points to a Virtual Block Mapping object, wherein the Virtual Block Mapping object includes another mapping pointer to refer to a data block and a total distributed weight indicating whether the Virtual Block Mapping object has been shared.
 15. The system of claim 10, further comprising: third logic determining, based on the evaluation of I/O activity of the first and second data objects, whether to keep the first data object as a master deduplicated data object; fourth logic updating, based on the determination, a Virtual Block Mapping object referred to by a mapping pointer of the second data object by changing the mapping pointer included in the Virtual Block Mapping object to point to a Virtual Block Mapping object referred to by a mapping pointer of the first data object; and fifth logic freeing the second data object.
 16. The system of claim 15, further comprising: sixth logic updating a total distributed weight of the Virtual Block Mapping object referred to by the mapping pointer of the first data object.
 17. The system of claim 10, wherein a master deduplicated copy is selected from the group consisting of the first and second data objects based on evaluation of the I/O activity of the first and second data objects.
 18. The system of claim 10, wherein the first data object is selected as a master deduplicated copy upon determining that I/O activity of the first data object is more than I/O activity of the second data object. 